1. Field of the Invention
The present invention relates generally to a method and an apparatus for opening crimped TOW to prepare opened continuous filaments, to be used as a surface layer of an absorbent article, such as sanitary napkin, or for other application.
2. Description of the Related Art
For a surface layer of an absorbent article, such as sanitary napkin, conjugated synthetic fibers of core-sheath structure, such as those of PE/PP, PE/PET or the like are used. As the conjugated synthetic fibers, continuous filaments may be used.
The continuous filaments are supplied to a manufacturing process of absorbent article or so forth in a form of TOW, in which filaments are bundled to firmly contact with each other and are crimped. In the manufacturing process, opening process is preformed to separate the continuous filaments from each other in the width direction of the TOW and to increase apparent width. The continuous filaments thus separated in the width direction in the opening process to have a uniform bulkiness, are used for production of the surface layer of the absorbent article or the like.
Conventionally, the following method is employed for opening the TOW.
At first, the TOW is supplied to a transporting roll group which is constructed such that downstream side roll has higher peripheral speed than that of upstream side roll for applying tension force to the TOW between the rolls. Then, the TOW is transferred to a transporting roll group which is constructed such that downstream side roll has lower peripheral speed than that of the upstream side roll for releasing the tension force. Application of tension force and release of tension force are effected, respectively at least one time. In this method, the tension force is applied to the continuous filaments forming the TOW for stretching crimp, and then, the filaments are elastically contracted to restore crimp. By stretching crimp and restoring crimp, the continuous filaments are given dispersing force in the width direction of the TOW.
As an alternation, there is another method for opening the TOW, in which a threaded roll formed with circumferentially extending grooves at a given pitch in the axial direction, is driven to rotate and the TOW is supplied onto the surface of the rotating threaded roll for opening. In this method, tension forces to be applied to the continuous filaments are varied between portions of the threaded roll where the grooves are present and portions of the threaded roll where the grooves are not present. By variation of tension force, the continuous filaments forming the TOW are locally stretched and locally contracted and whereby to apply dispersion force in the width direction of the TOW.
In the further alternative, there is still another method for opening the TOW, in which an air jet is applied along longitudinal direction of the TOW. In this method, by blowing force of air, dispersing force of the continuous filaments is applied in the width direction of the TOW.
However, in the method where different peripheral speeds are provided for rolls in the transporting roll group, opening condition of the TOW depends on the peripheral speeds of the rolls, nip pressure of the rolls, materials of the roll surfaces and the like. Similarly, in the method employing the threaded roll, opening condition depends on nip pressure of the roll, material of the surface of the roll, size of each groove and the like.
Accordingly, when bundling condition of the TOW, basis weight of the TOW, fineness of continuous filaments or material of continuous filaments is varied, optimal opening may sometimes be impossible under the same condition. In such case, preparatory operation for varying various conditions is quite difficult and huge amount of cost is required for varying facility configuration.
On the other hand, in the method where the TOW is opened by air jet, since continuous filaments are separated by air flow, it is difficult to achieve uniformity in opening.